Over voltage
An abnormally high voltage sustained for an extended period.

Phase
Load current is drawn from a voltage source. In ac systems,
the voltage is a sine wave and for a purely resistive load,
the current drawn is also a sine wave aligned perfectly (in
phase) with the voltage sine wave. Most loads, however, are
not purely resistive and the current drawn is delayed and lags
behind the voltage sine wave (out of phase). The lag is
measured in degrees. Power factor is equal to the cosine of
this phase difference.

Power Factor
The relationship between actual power (W) and apparent power
(VA). Calculated by dividing Watts by Volt-Amperes (W/VA) and
usually in the range of 0.75 to 0.85.

PWM – Pulse-Width Modulation
Process of varying the width of a train of pulses to adjust
the rms voltage and frequency and modify the waveshape,
typically to sinusoidal.

Rectifier
/ ChargerPart of a UPS that converts the incoming ac utility
power to dc power for the inverter and to charge the
batteries.

RFI – Radio-Frequency Interference
Electrical noise resulting from some parts of the equipment or
wiring acting as a radio antenna. This noise may be large
enough to disrupt communications or cause computing error.